In order to prove the correctness of the power control method, a prototype of a one-to-three non-contact charging device was designed. It is mainly composed of a switching power supply, a source transmitting coil, three receiving coils, a rectifying voltage regulator circuit, and a load device (a lamp, a fan, and a camera) after each coil. Figs. 7 and 8 are the matching circuit structures of the transmitter and receiver, respectively. A cement board is used between the transceiver terminals instead of the wall in the actual use.
The input voltage of the switching power supply is 12 V. The digital signal source converts 50 Hz commercial power into 130 kHz high-frequency alternating current. The transmitting coil converts electric field energy into magnetic field energy. The transmitting and receiving coils are coupled, so the magnetic field can penetrate the wall and be coupled to the receiving end. It converts magnetic field energy into electric field energy. During the test, the load devices at each receiving end are different, and the coil size is also different. That is to say, the key parameters of the wireless energy transmission system have different load impedance and coupling coefficients, so that precise power control and power distribution are required. At the same time, the matching capacitors on both sides of the transceiver are optimized. Table 1 shows the performance parameters of each coil in the system.
Transmitter coil Lamp coil Camera coil Fan coil Self-inductance (μH) 178.08 42.19 24.72 51.50 Capacitor Cp1 (nF) 4.72 21.60 37.44 16.21 Capacitor Cp2 (nF) 11.20 24.10 8.92 9.88 Size (mm) 470.0×340.0×2.5 R40.0×1.2 R70.0×2.0 R70.0×2.0 Coupling coefficient — 0.120 0.162 0.182 Operating frequency (kHz) — 150 — —
Table 1. Parameter of this system
The rated power of the three receivers (lamp, camera, and fan) is 1.5 W, 5.0 W, and 6.0 W, respectively, and the working voltage under the rated power is 5 V, 5 V, and 12 V, respectively, which can be seen from Figs. 9 and 10. The input DC voltage of the transmitter is 20.5 V, the current is 1.1 A, the power is 22.55 W, and the three receivers are fully loaded. The total output power of the system is 12.5 W and the system’s working efficiency is 55%.